The Boston Marathon bombings, still of unknown provenance, send a special chill through New York City, where precautions against attack have commanded municipal attention for nearly 12 years.

Any impact on the mayoral race here remains a matter of mood and flavor. The perennial conversation about balancing order and freedom takes on a more constrained tone.

On Monday night, Comptroller John Liu -- the only one of five mainstream Democratic candidates vowing to end, rather than tweak, police stop-and-frisk policies -- reacted cautiously to the Boston catastrophe.

"These are very complicated matters," Liu said after a Democratic candidates' forum at the College of Staten Island. "And I think in New York we've done a very good job to fight the potential terrorist threats."

Former Comptroller Bill Thompson, who pushes for some restoration of the NYPD ranks, took a similar tack. "We're waiting for facts," he said. "To jump to conclusions right now would be wrong. . . . You're going to hear a lot more, certainly, once we get more facts."

The current administration at City Hall stood in a sort of informational holding pattern as well. By midafternoon yesterday, Mayor Michael Bloomberg and Police Commissioner Ray Kelly were reinforcing what they'd said in the hours immediately after the fatal bombings at the Boston Marathon.

Even with no local threats, Kelly said "we've prepared as if yesterday has been a prelude to an attack in New York" -- as has been procedure since 9/11.

City Council Speaker Christine Quinn urged the Staten Island audience in closing remarks, "Let's just remember to say a prayer for the people of Boston, particularly for the people who died today, or were injured, and those who have lost family members to this terrible act of terror."

A moment of silence was observed in the auditorium at the outset.

"As I was leaving to come here, I saw on the news that one of the victims was an 8-year-old child," said Public Advocate Bill de Blasio. "And everyone in this room knows the feeling, that we're going to be in a long-term fight to make sure everyone's safe and secure, and that's what those of us in government have to devote ourselves to."

What else was anyone in the public life of the state or city going to say or do?

Which is not to say the usual debate over city problems -- failing schools, spotty transportation, closing hospitals and unaffordable housing -- was suspended. Some of the discussion involved a different fatal catastrophe, the damage wrought by superstorm Sandy.

Nor was the occasion levity-free. Quinn went for some local pride with the wrap-up joke that the groundhog Staten Island Chuck could become an "economic development engine," and "we could take down that Punxsutawney Phil."